The invention relates generally to electrostatic precipitators and more specifically to a system and method for detecting partial discharge activity in electrostatic precipitators and their components.
Many industrial operations produce exhaust gases that contain dust, fly ash (unburned constituents from burning), fumes (fine elemental particles such as cadmium, sulfur and lead) and mist (such as coal tar), which are undesirable for the environment. One widely used method of removing such contaminants from a gas stream is to use an electrostatic precipitator.
In one example, electrostatic precipitators are composed of metallic plates subjected to a potential difference in order to exploit the corona activity and capture the electrostatically charged dust of the smoke exiting from the smokestack of a factory. The plates are bumped at regular intervals (for dust removal), and the dust is then collected at the bottom of the electrostatic precipitators. Because higher voltages result in more efficient dust collection, the voltage is typically increased until sparking, i.e. electrode short-circuit, occurs. Such sparking then causes the voltage to drop off, and the process of starting at a low voltage and ramping to a higher one starts. During the voltage drop off, dust is not collected, and emissions increase. Sparks sometimes result in damage of the electrode surface which can lead to failure of the electrostatic precipitator. Most customers retain their electrostatic precipitators as a primary or a secondary device for emission control. The electrostatic precipitators are also recently being considered for integration into future mercury and sulfur solutions as well for lighting industry. Thus it is increasingly becoming important to have better operating and maintenance procedures for electrostatic precipitators.
Partial discharge analysis is a non-destructive and a non-invasive testing technique to detect different defect types in materials. A partial discharge is a localized electric discharge in which the distance between the two electrodes is only partially bridged. In other words, partial discharge refers to the dissipation of energy caused by the localized build-up of an electrical field in an insulating material. Partial discharges are most commonly observed in medium to high-voltage devices such as transformers, cables and generators. In these devices, occurrence of partial discharges can be indicative of insulation deterioration. Partial discharges can also cause further deterioration of the insulating dielectric material. Early detection of partial discharges helps prevent insulation breakdown, avert damage of insulation systems, extend the lifetime of the insulation, and help in efficient maintenance planning.
Different dielectrics and insulation systems have different partial discharge signatures. In rotating machines for example, partial discharge analysis has been used in the past to define material defects such as delaminations in conductors and insulators, winding armor degradation, voids, contamination, and corona suppressor damage. Although partial discharge analysis is a powerful tool, its use has been limited as a tool for detecting material defects.